The present invention relates to grain milling. More particularly, the present invention relates to tanks for the steeping of grain.
Grain steeping tanks are used in the hydration of grains to soften the grain for milling. In a conventional grain steeper, grain is soaked in a liquid for a sufficient period of time to allow the grain to soften prior to refining and milling procedures to separate the grain into component parts. A conventional grain steeping vessel is a large tank on the order of ten feet in diameter and extending upwards to sixty feet or more. The tank is filled with a mixture of grain, water and SO.sub.2. The SO.sub.2 aids in the absorption of water by the grain, most typically corn. The SO.sub.2 is at least partially consumed in the steeping process. Once the steeping vessel is filled, it is sealed from atmosphere. The grain is allowed the steep for as long as forty hours to fully soften the grain. The steeping time, however, has been decreased to as little as 32 hours to speed up the milling production process. This reduction in time has been accompanied by a reduction of the quality of the steeped grain, because the steeping process has not improved. The result has been that the grain has been transferred to the milling process in a form harder than would be preferred for optimum milling.
In the conventional grain steeping apparatus, the grain and liquid mixture has been allowed to simply rest. However, this results in uneven and incomplete steeping of the grain. The steeping process involves the grain absorbing water. This water absorption aids in the process of breaking the grain into its component parts during subsequent milling. As the grain steeps in a conventional steeping apparatus, the grain sticks together. Those areas of grain-to-grain contact resulting from sticking receive insufficient contact with the liquid mixture to result in complete and uniform hydration of each individual kernel. In addition, due to the tall height of some of the steeping vessels, grain located at the bottom of these vessels experiences significantly higher fluid pressures than grain located at the top. The grain at the bottom experiences both higher fluid pressure and less exposure to the fluid mixture because of the increased grain-to-grain contact due to the pressure. The result is that between the top and the bottom of a conventional grain steeping vessel, corn does not experience uniform steeping.
There have been some efforts to improve the steeping process. The addition of SO.sub.2 to the water does increase the rate of steeping, however, the steeping enhancing effect of the SO.sub.2 plateaus at higher concentrations of the additive. In addition, SO.sub.2 is a relatively caustic and corrosive material, therefore requiring extra safety procedures and vessels able to withstand the corrosive effect of the material.
Efforts have been made to recirculate the liquid mixture through steeping vessels to increase the uniformity and speed of the steeping process. Such recirculation methods have not effectively dealt with the issue of grain-to-grain contact and pressure differentials within large steeping vessels, and so have had limited effect of improving steeping.
A further concern for the proper steeping of grain is the maintaining of the grain kernel integrity. If the kernel is broken open prior to milling, valuable starches will be lost from the refining process. Any improvement in steeping cannot therefore be at the expense of damaging the hull of the grain.
Additionally, millers have a large capital expenditure in their present steeping equipment. Any improvement in steeping would be most economically feasible if it allows retrofitting of existing steeping equipment. The new equipment should also be simple to operate and maintain so as not to increase costs of production.